This application relates to the field of door access security systems and, particularly, to the field of card readers for door access security systems.
Door access security systems, utilizing magnetic card readers at doors to be controlled, are known in the prior art. Such systems include central controllers coupled to a plurality of readers, each of which is located at a specific door to be controlled. Authorized persons wishing to gain access through a door, insert magnetic cards into slots in the reader. Magnetic codings on the cards are then read and data is sent to the controller which authorizes or refuses entry and tells the reader either to keep the door locked or unlock the door.
Such a system can advantageously be used as a time clock to keep a record of the hours worked by hourly employees. However, a problem with system throughput arises when a large number of employees all try to clock in or out at the same time. The delays caused by reading of a card, waiting for a poll signal to come to the reader from the controller, sending the card data to the controller and waiting for the controller to process the information and send back a "Go" or "No Go" signal can create impatience in the workers at the end of the line.
Such card reader systems can also be used to monitor alarm contacts located at strategic locations throughout a facility. In the prior art, a centrally located alarm contact monitoring device was located near the controller with individual wires coupling the contact monitoring device to the alarm contacts located throughout the plant. Such systems were effective but required an individual polling protocol and the associated hardware for the alarm contact monitoring device. Further, individual wires had to be strung between all the contacts to be monitored and the central monitoring device. This could result in large expenditures for wire. Further, such central contact monitoring devices were generally not well suited to applications where only a single alarm contact needed to be monitored since the function rarely justified the expense.
The prior art systems also had room for improvement in the area of operation during times when the communication lines between the reader and the central controller were down. In such a situation, if all access was denied, people would be inconvenienced or, worse, trapped in an undesirable emergency situation. The alternative would be to allow free access through all doors. However, with record-keeping functions done at the central controller, there would be no record of the individuals who entered and left specific areas during specific times while the lines were down. As a result, if theft occurred during the down time, there would be no record to use in the investigation.